1. Field of the Invention
This invention relates to the processing of metal chlorides and the recovery, therefrom, of metal.
2. Brief Description of the Prior Art
Titanium tetrachloride may be produced by chlorinating a titaniferous material which, typically, contains at least 90% by weight of titanium dioxide either because it comprises a titanium-rich ore such as rutile or because it comprises an ore beneficiate or synthetic rutile from which a large proportion of the iron originally in the ore has been removed. The chlorination is followed by the purification of the titanium tetrachloride vapour produced and the accumulation in the course of such purification of one or more residues which, typically, contain iron compounds but which may also contain chlorides of high value metals, such as niobium or vanadium and chlorides of relatively low value metals such as aluminium, magnesium, calcium and manganese.
Particularly, in the chlorination of a titaniferous ore such as rutile or synthetic rutile ore, in a fluidised bed in the presence of carbon the stream of gases issuing from the fluidised bed contains
1. Blow-over dust, e.g. TiO.sub.2, C, SiO.sub.2, ZrO.sub.2, ZrSiO.sub.4.
2. Vapourous chlorides of the minor constituents of the ore.
3. Residual inert gas and carbon oxides.
4. Titanium tetrachloride vapour.
This effluent stream may be cooled to condense some of the chlorides, notably iron chlorides and niobium chloride, without condensing any substantial quantity of titanium tetrachloride and passed to a cold cyclone where such condensed materials and blow-over dust are substantially removed from the stream. The titanium tetrachloride may then be condensed to separate it from residual inert gases and carbon oxides and purified by treatment with mineral oil, a mineral oil sludge residue often containing aluminium chloride, niobium chloride and vanadium chloride thereby being produced.
It would be desirable to recover the high value metals from metal chloride residues. Particularly, the cyclone and oil purification residues from titanium tetrachloride production, combined or separately, provide a relatively concentrated source of high value metals, e.g. niobium and/or vanadium, if they can be recovered effectively and economically from the chloride form in which they are present in the residues and, preferably, fractionated to some extent from the low value metals also present. A typical combined cyclone and oil purification residue from a titaniferous ore chlorination process for the production of titanium tetrachloride can contain, for each mole of titanium tetrachloride produced, up to about 0.0075 moles of vanadium chloride and up to about 0.005 moles of niobium chloride and, assuming the producing unit to be on a commercial scale, the equivalent annual quantities of vanadium metal and niobium metal present in the residue amount of hundreds of tons.
British Pat. No. 1,250,913 relates to a process for treating a vanadium, zirconium or chromium-containing residue from the chlorination of titaniferous ore, to facilitate the recovery of vanadium therefrom, comprising treating the residue with water in an amount insufficient to slurry the residue but at least sufficient theoretically to react with all the chlorine of the residue and heating the so-treated residue in a free oxygen-containing atmosphere at a temperature of at least 300.degree. C. to remove the major part of the chlorine as hydrogen chloride to ease the recovery of vanadium, zirconium or chromium as oxides. The said recovery is a chemical process involving treatment with an alkali or acid to provide solutious which, by conventional techniques, give rise to the separate constituent metals.
The U.S. Bureau of Mines Report R1 7671 (1972) describes a process for the separation of columbium (niobium), tantalum, titanium, and zirconium from mineral waste from the chlorination of rutile ore. The process described is a liquid-liquid extraction process involving the use of a 10-stage reactor.